1. Field of the Invention
The present invention generally relates to externally controlled fan coupling devices for controlling the rotation speed of a fan for cooling an engine of an automobile or the like in accordance with changes in the ambient temperature or changes in the rotation.
2. Description of the Prior Art
There is a conventional fan coupling device of this type in which the interior of a sealed housing constituted by a case and a cover is separated by a partition plate having an oil supply adjusting hole into an oil reservoir and a torque transmission chamber having a driving disk contained therein; a dam and a circulation channel contiguous to the dam that establishes communication from the torque transmission chamber to the oil reservoir are formed on a part of an inner circumferential wall of the sealed housing opposite to an outer circumferential wall of the driving disc on which oil collects during rotation; and a valve member is provided for opening the supply adjusting hole on the partition plate when the ambient temperature exceeds a set value and for closing the supply adjusting hole of the partition plate when the temperature is equal to or lower than the set value to control the transmission of torque from the driving side to the driven side of the sealed housing by increasing and decreasing an effective contact surface of oil at a torque transmitting gap provided between the driving disc and a wall of the sealed housing opposite thereto located in the vicinity of the exterior thereof. A pair of electromagnets are provided on a front surface or rear surface of the sealed housing; a magnetic valve member for opening and closing the supply adjusting hole is provided opposite to one of the electromagnets; and a magnetic sub valve member for opening and closing the circulation channel is provided opposite to the other electromagnet (see Japanese patent No. 2911623).
In general, such a conventional externally controlled fan coupling device has problems in that it has a complicated mechanism, consumes great power, and results in a high cost because it is primarily electrically controlled and in that the fan coupling device can be damaged because of disablement of circulation of operating oil due to a failure of the electrical system. However, since an externally controlled fan coupling device is advantageous in that controlling factors such as the water temperature, the engine speed, and auxiliary devices such as an air conditioner can be arbitrarily selected and in that adequate fan control can be performed, demands have existed for improvements for solving the above-described problems.
The invention has been made taking such a situation into consideration, and it is an object of the invention to provide an externally controlled fan coupling device which has a simple mechanism to allow saving of power consumption, which has a xe2x80x9csafety onxe2x80x9d function (a function of allowing operating oil to be circulated without being stopped even in the case of a failure of an electrical system) and which can freely and properly control the rotation speed of a fan by accurately adjusting the amount of oil in accordance with various operating conditions.
The present invention basically employs a method in which a valve member for opening and closing an oil supply adjusting hole for supplying operating oil from an oil reservoir to a torque transmission chamber is controlled by a non-excited electromagnet that utilizes a permanent magnet. In principle, there is provided a fan coupling device in which the interior of a sealed housing constituted by a case supported and born by a rotary shaft body having a driving disc secured to an end thereof through a bearing and a cover attached to the case is separated by a partition plate having an oil supply adjusting hole into an oil reservoir and a torque transmission chamber having the driving disc contained therein; a dam and a circulation channel contiguous to the dam that establishes communication from the torque transmission chamber to the oil reservoir are formed on a part of an inner circumferential wall of the sealed housing opposite to an outer circumferential wall of the driving disc on which oil collects during rotation; and a valve member is provided in the oil reservoir for opening and closing the oil supply adjusting hole to control the transmission of rotation torque from a driving side to a driven side by increasing and decreasing an effective contact surface of oil at a torque transmitting gap defined by the driving side and the driven side, characterized in that a non-excited electromagnet utilizing a permanent magnet located in the oil reservoir of the sealed housing is supported around the rotary shaft body through a bearing to actuate the valve member with the electromagnet, thereby providing a mechanism for controlling the opening and closing of the oil supply adjusting hole.
The invention is also characterized in that a plurality of the oil supply adjusting holes are provided to form a double valve structure in which a valve member is provided for each of the oil supply adjusting holes.
The permanent magnet may be attached to either the sealed housing or electromagnet or to both of the sealed housing and electromagnet. The valve member may be constituted by a plate spring and a magnetic piece, and it may alternatively be constituted by a coil spring and a magnetic piece. Further, the invention is characterized in that the case may be made of a non-magnetic material.
According to the invention, the mechanism for controlling the opening and closing of the valve member which employs a system for controlling the opening and closing of the oil supply hole using the non-excited electromagnet utilizing a permanent magnet has the same principle as that of a common non-excited actuation valve. According to the principle, when a current is applied to the electromagnet to generate a magnetic field in a direction opposite to that of a magnetic field generated by the permanent magnet, the magnetic field of the permanent magnet is cancelled, and the attracting force of the permanent magnet is extinguished, which provides a mechanism for closing the oil supply adjusting hole by urging the valve member against the partition plate through the action of the spring and for opening the oil supply adjusting hole by turning the electromagnet off to attract the valve member toward the permanent magnet against the spring.
By applying a current to the electromagnet to generate a magnetic field in the same direction as that of a magnetic field generated by the permanent magnet, the oil supply hole can be instantaneously opened as a result of a synergistic effect of the attracting force of the permanent magnet and the attracting force of the electromagnet.
Therefore, the use of the opening/closing control mechanism makes it possible to maintain a xe2x80x9csafety onxe2x80x9d state or a state in which the oil supply adjusting hole provided on the partition plate is kept open even when the electromagnet is turned off due to a failure of the electrical system, which allows the operating oil to be circulated, keeps the fan coupling device on to cause the fan to continue rotating, and makes it possible to prevent damage to the engine due to overheating.
When a plurality of the oil supply adjusting holes are provided to form a double valve structure, the magnitude of the current for energizing the electromagnet may be varied stepwise to open and close each of the valves stepwise, which makes it possible to increase the rotating speed of the fan stepwise or to change the rate of the speed increase.
The case is made of a non-magnetic material to prevent leakage of magnetic flux. In the case of a case made of iron, a part of the case is cut off to prevent leakage of magnetic flux, and the same part is sealed with a sealant.